Set Appliance State:

Mains Power Off
Preheat switched OFF (ECO button illuminated)
Turn hot water tap on with a flow rate of approximately 3 l/min
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance as necessary (hold reset button for 5 seconds then release).
Can the burner be heard to ignite and establish?
Note:
On some versions the flame can be seen via the viewing
window at the top of the heat exchanger.